The coefficients ar and br from Eq. (14) were estimated by linear regression to be 6.3 × 10−4W−1min−1 and 1.05 × 10−3 ◦C−1min−1, respectively. A non-linear model of the form below (Eq. (15)) was therefore proposed to describe the dependence of WGR on drying time, micro wave power and air temperature.